GB362355A - Improvements in or relating to apparatus for switching out faulty electric line sections - Google Patents

Abstract

362,355. Protective cut-out arrangements. SIEMENS-SCHUCKERTWERKE AKT.-GES., Siemensstadt, Berlin. Aug. 27, 1930, No. 25583. Convention date, Aug. 29, 1929. [Class 38 (v).] A protective arrangement for cutting out a doubleearth fault on a sectionalized line having an insulated neutral, comprises a series of circuit-breakers under control of relays a .. g, each of which comprises a spring-controlled disc 1 acted on by windings 3, 4, connected, respectively, in the residualcurrent circuit of current transformers 5, 6, 7 in the lines R. S, T, and to series-connected secondaries 12, 13, 14 of potential transformers having an earthed neutral 11. In the event of a doubleearth fault occurring at I, II in the lines S, T, Fig. 2, the appropriate windings 20 of relays c, d, e will close their contacts 19 to energize coils 17 which unlock the discs 1 of those relays. The out-of-balance current appears in the windings 3 of those relays, and the potential between the starpoint of the lines and earth appears in the windings 4. Owing to the phase-displacement between the current in winding 3 and the potential in winding 4 of relay e being greater than at relay d, the relay e will be the first to close its contacts 22 and trip the breaker 28, so cutting out the double-earth. The single-earth fault current remaining is not ordinarily in excess of normal working current, as it is the capacity current of the lines to earth, and even if it is in excess of such normal current, the windings 20 are made insensitive to it. It may, however, be dealt with, if desired, in other ways. A short-circuit relay 25 is also provided, but its trip circuit is opened at 26 when a disc 1 begins to move. The energization of winding 4 may, alternatively, depend on interphase voltages having fallen below a given value, and a further interlock may be provided, to be released only on excess current in more than one phase.